Java(TM) Web Start Launcher doesn't work after a software update for some users

Hello;

We've ran into a problem where we have an application that is hosted on a server that uses web start. Normally the web start link works, except after the product has been upgraded to the next version. Some users can download the new jars with the web start link and upgrade seamlessly, but others get an "unable to launch the application" error. Those users then have to go back to the web site where they originally downloaded the application from and get the upgraded application and upgrade their short cut.
Is this a know issue and if so is there some workaround so that all users can use the web start link to get the new jars?